Characterization of wet-mix shotcrete for small line pumping

With the increasing need for concrète repairs and the increasing knowledge available today in shotcrete technology, shotcreting is in great demand. Considérable work has been done over the last décade in terms of shotcrete fundamentals and properties for the dry-mix shotcrete process. Unfortunately, few research projects have focused on the fundamental knowledge of the vvet-mix shotcrete process. With the growing demand of wet-mix shotcrete as a repair material and the industry turning towards small line pumping, there is a serious need for reliable expérimental data along with a fundamental understanding o f this p l a c e m e n t m e t h o d . The objective of this research project is to improve our understanding of the mechanisms involved in the mixing, pumping and placement o f wet-mix shotcrete. A better understanding will allow the development o f the necessary knowledge that will help engineers to specify, use and control wet-mix shotcrete in rehabilitation and repair applications. Following a review of the information available, the objective will be reached by focusing mainly on the following: Apply scientific methods to the design of concrète mixture in order to improve wet-mix shotcrete in terms o f the robustness in maintaining fresh properties over time in order to accommodate delays, warm températures or concrète pumps with small diameter hoses. The latter receiving the most attention. Investigate the fundamental properties and placement kinetics o f fresh wet-mix shotcrete to identify stratégies to mcrease maximum build-up thickness and minimize rebound without using set accelerating admixtures. Inquire into the effects of air in the mixture and the effect o f pumping on the air void System charactenstics in order to introduce this knowledge to existmg pumpability prédiction models. The originality of this project is the focus on complex problems and solving them through a solid scientific approach. It is only through a fundamental understanding of the behavior of the material in its liquid and solid states associated to the transpoliation and placement phases that true compréhension, optimization and improvement of the wet-mix shotcrete method will be possible.